Method of making electrical cables

ABSTRACT

A method of making electrical cables having an outer shielding element of thin metal tape; the tape being shaped into tubular form about the cable core and having a longitudinal seam; the seam having marginal tab portions integral with the tape and in face to face contact, the outer edges of the tab portions being metallically integrated to provide electrical conductivity continuously about the circumference thereof and to form a fluid impervious envelope for the core which is resistant to mechanical stresses.

United States Patent 1 Ziemek METHOD OF MAKING ELECTRICAL CABLES [75] lnventor: Gerhard K. Ziemek, Hannover,

Germany [73] Assignee: Kabel-und Metallwerke Gutehoffnungshutte Aktiengesellschaft, Hannover, Germany 221 Filed: 0ct.6, 1970 211 App]. No.: 78,386

Related US. Application Data [62] Division of Ser. No. 864,984, Oct. 9, 1969, Pat. No.

[52] US. Cl 29/624, 156/54, 174/102 R,

I 174/l07 R [51] Int. Cl. H01b 13/26 [58] Field of Search 29/474.1, 624; 174/102 R, 105 R, 107 R, 36; 156/54 [56] References Cited UNITED STATES PATENTS 2,543,668 2/1951 Penrose et al. 29/624 UX Oct. 23, 1973 2,639,633 5/1953 Sowter 174/102 R X 2,936,357 5/1960 Crawford 174/102 R X 3,136,676 6/1964 Fisch 29/624 UX 3,332,138 7/1967 Garner 29/624 X FOREIGN PATENTS OR APPLICATIONS 863,684 4/1953 Germany 174/102 910,072 7/1954 Germany 174/102 Primary Examiner-Charles W. Lanham Assistant Examiner-Joseph A. Walkowski Attorney-Philip G. Hilbert [5 7] ABSTRACT A method of making electrical cables having an outer shielding element of thin metal tape; the tape being shaped into tubular form about the cable core and having a longitudinal seam; the seam having marginal tab portions integral with the tape and in face to face contact, the outer edges of the tab portions being metallically integrated to provide electrical conductivity continuously about the circumference thereof and to form a fluid impervious envelope for the core which is resistant to mechanical stresses.

3 Claims, 8 Drawing Figures PAIENTEH um 23 was SHEET 1 0F 2 INVENTUR. erhrdk Z/ e/wk ATTORNEY PAIENIEDHCI 2 I915 3.766.645

- sum 2 OF 2 METHOD OF MAKING ELECTRICAL CABLES This application is a division of application Ser. No. 864,984, filed Oct. 9, 1969, now US. Pat. No. 3,576,939.

The increasing trend toward locating communications cables in the ground has made it necessary to provide means for protecting the buried cable from the ingress of moisture. This can be accomplished by enclosing the cable core in an impervious metal envelope or by filling the cable core with a waterproof flooding compound; or a combination of such procedures.

The metallic envelope, in addition to serving as a moisture barrier, must also provide the required electrical conductivity to allow the same to function as a shielding means.

The instantinvention is concerned with a thin metal sheath or covering for a cable core, preferably of aluminum, which combined vapor imperviousness, corrosion resistance; good shielding characteristics and mechanical properties facilitating the flexing and reeling of the cable.

A number of sheath designs have been proposed which purport to satisfy the aforementioned requirements. Thus, in one case, it is proposed to use aluminum tapes coated with monomer modified polyethylene resin which is highly adherent to the metal. The tapes are longitudinally folded about the cable core with the edges overlapped and heat sealed. Usually, inner and outer jackets of polyethylene resin are fused to the coated tape.

In another case, a double sheath construction is proposed, wherein the inner sheath consists of aluminum tape of at least 0.661 inch thickness and coated on opposite sides with polyolefin resin. The sheath forming tape is loosely folded about the cable core and the marginal edges of the tape are bent to form radially extending tabs which are heat sealed through the intervening resin coatings. The projecting sealed tabs are then folded over against the sheath and an outer sheath is then applied. The outer sheath constructions are known in the art under the designations of 'Alpeth, Stalpeth or FPA.

The instant invention constitutes a further development of known thin walled metal envelopes for cables wherein a metal tape is formed in tubular shape about the cable core, the edges of the tape being brought into abutting relation, and welded together. The resultant envelope is then drawn down or transversely corrugated to provide a tight fit between the sheath and the cable core.

However, it has been found that with metal tapes having a thickness of 0.010 inch or less, the forming and butt welding operations present difficulties, particularly in the case of larger core diameters. This is due to a lack of form stability of the thin metal tape and variations in metal thickness in commercially available tapes.

It has also been proposed to provide metal sheathing by welding overlapped edge portions of the thin metal tape folded about a cable core. This method is reasonably applicable to copper tapes but can not easily be used with aluminum tapes due to the presence of oxide layers on the overlapped tape surfaces. Such oxide layers make it exceeding difficult to obtain a sound, uniform metallic bond therebetween.

Accordingly, an object of this invention is to provide an improved sheath or covering in electrical -cables which overcomes the disadvantages of known constructions. More particularly such sheath provides a thin walled metal envelope for the cable core wherein the envelope includes a longitudinal seam comprising facing, radial tab portions which are metallically integrated to make the seam impermeable to fluids; highly resistant to mechanical stresses under severe conditions of handling and installation; and further, to provide continuous circumferential electrical conductivity to significantly enhance the shielding characteristics of the cable.

A further object of this invention is to provide a cable sheath which is formed of very thin metal tapes, including aluminum tapes, wherein the tape is folded about the cable core to accommodate any irregularities in the surface portions of ,the core; the tape having sufficient width in relation to the circumference of the core, to provide marginal tab portions which are brought into face to face contact; the outer edges of the tab portions being trimmed to leave the tab portions at a predetermined height, with such edges coextensive and presenting freshly cut, oxide free edge surfaces which are immediately thereafter welded or otherwise metallically integrated.

Another object of this invention is to provide a thin metal sheath or covering of the character described, wherein the outer surface of such sheath has applied thereto a metal adherent synthetic resin which renders the sheath corrosion proof, together with a protective jacket of synthetic resin applied over the metal adherent resin and bonded thereto.

Yet a further object of this invention is to provide a sheath or covering for electrical cables of the character described, wherein such sheath or covering may be formed of exceedingly thin metal tapes which minimizes metal requirement; which may be stiffened by the resin coatings applied thereto to resist mechanical stresses; and which shows excellent shielding characteristics.

Still another object of this invention is to provide improved cable constructions of the character described, wherein the sheath or covering is formed of metal tape folded about the cable core to provide tab portions in face to face relation and initially radially disposed for metallic integration of their edges; the metal tape having minimal thickness which permits the cable, after folding the tab portions downwardly against the sheath, to be readily flexed, reeled and unreeled.

Yet another object of this invention is to provide cable constructions of the character described and having a sheath showing enhanced shielding characteristics, making the same particularly useful in communications cables where interference exteriorly and interiorly thereof must be eliminated or minimized.

Yet a further object of this invention is to provide improved electrical cables of the character described, wherein the tab seam portions thereof may be folded or otherwise manipulated to facilitate cable splicing operations, cable suspension and to provide a variety of cable configurations.

Still another object of this invention is to provide improved methods of forming electrical cables having a thin metal sheath with a longitudinal seam having radial tab portions with oxide free edges metallically integrated to provide continuous electrical conductivity circumferentially of the sheath.

Other objects of this invention will in part be obvious and in part hereinafter pointed out.

FIG. 1 is a transverse sectional view showing an electrical cable having a sheath or covering embodying the invention; i

FIG. 2 is a view similar to that of FIG. 1, showing another embodiment of the invention;

FIG. 3 is a view similar to that of FIG. 1, showing a further embodiment of the invention;

FIG. 4 is a view similar to that of FIG. 1, showing still another embodiment of the invention;

FIG. 5 is a side elevational view schematically showing apparatus for forming cable of the instant invention;

FIG. 6 is a transverse sectional view taken on the line -66 of FIG.=5;

FIG. 7 is a sectional view taken on the line 7-7 of FIG. 5; and

to coating 20, and will provide adequate protection to the coating being spaced from edges 18 of the strip, to

FIG. 8 is a sectional view taken on the line 88 of FIG. 5.

The instant invention is concerned with a method of making electrical cables embodying tubular sheaths or coverings of thin metal tape for the cable core or cores thereof to' exclude tne entry of harmful liquids, vapors or gases therein; the sheath or covering being highly resistant to mechanical stresses and showing excellent shielding characteristics.

The coverings are formed from metal tapes having a wall thickness not exceeding about 0.30 mm; the metal being preferably aluminum; although copper, steel or other metals and alloys thereof, may also be used.

Thus, as shown in. FIG. 1, l0 designates an electrical cable having a conventional core 11 made, up of the usual insulated conductors. The core 11 is enclosed in an envelope 12 formed from a metal strip 13 which is folded about core 11.

Strip 13, of aluminum, has a width greater than the circumference of core 11, soas to provide a longitudinal seam portion 14 comprising marginal portions 15 of the strip 13 which are bent from edge portions 16, 17 to dispose portions 15 in radially extending, tab form, said portions 15 being in face to facecontact'.

The tab edges 18 are coextensive throughout their length, such edges being trimmed by cutting to a predetermined tab height. The resultant oxide free edges 18 are metallically integrated by a continuous, longitudinal weldment l9 bridging said-edges. I I

The upstanding tab seam 14 may be folded over at edges l6, 17 to dispose the same against the outer surface of envelope 12; as indicated in the dotted lines. Thus, the cable 10 may be readily flexed for reeling, unreeling and installation.

As shown in FIG. 2, the cable 10A, is similar to cable 10, except that a coating 20 of syntheticresin highly adherent to metalis applied to the outer surface of envelope 12, as by extrusion, coating, electrophoretic deposition and the like. Such resin may be formed of copolymers of polyethylene and selected monomers, as described in US. Pat. Nos. 2,987,501 and 3,027,346. Coating 20 renders the envelope l2 highly resistant to corrosion and imparts some stiffness to the thin metal of the envelope. i

A jacketing coating 21 is applied over coating 20 by extrusion or the like; coating 21 being of polyethylene, polyvinyl chloride, or the like. Coating 21 will adhere locate coating edges 22 adjacent or abutting each other. Also, coating 20A, may be applied to the outer surface of strip 13, or to both surfaces thereof; such coating or coatings serving to render the envelope 12 resistant to corrosion.

Further, as shown in FIG. 4, the coaxial cable 30 comprises the usual inner conductor 31 which may be in tubular form and an outer conductor 32 held in concentric relation to inner conductor 31 by an intervening annular body 33 of synthetic resin foam, or other suitable dielectric spacing means.

'Outer conductor 32 is formed of metal tape 34 bent into tubular shape with a seam portion 35 made up of tab portions 36 metallically integrated as at 37, in the manner previously described. The tab seam 35'is bent over against the outer surface of the outer conductor 32. Metal adherent and jacketing resin coatings may be applied to cable 30, aspreviously described.

FIGS. 5 to 8 show an apparatus and method for making cable 10. The same comprises a forming table T along which'cable core 11 taken from a reel thereof, not shown, moves longitudinally, together with a metal tape M taken from a reel thereof, not shown, to a tube forming device 40, well known in the art and which foldsthe same intotubular form 13 about core 11 to form envelope12.

The tape M has a width greater than the circumference of cable core 11, so that the marginal portions thereof form the upstanding, radially disposed tab portions 15 in face to face relation. The assembly of cable core 11 and covering 13 move alongtableT to a trimming device generally indicated at 41, where the tab portions 15 are cut to a determined tab height, bringing freshly cut edges 18 thereof in a true alignment.

The assembly continues its movement past trimming device 41, the trimmed portion 42 of tab portions 15, being suitably removed; and bringing the fresh cut edges 18 thereofinto precise, measured alignment with suitable welding means 43, preferably operating under a protective atmosphere of argon or thelike, whereby to weld and metallically integrate tab edges 18 by way of continuous weldment l9 bridging said edges. The welding rate may be from about 5 to about 24 meters per minute with welding currents ranging from about 12 to about amperes.

The resultant tab seam 14, which may have a height of from about 4.0 mm to about 8.0 mm is folded over from its radial position by means of a suitable folding die 44. The coating 20 of metal adherent resin is applied by means of an extruder 45 while jacketing coating 21 is applied over coating 20 and in bonding relation thereto, by an extruder 46 or other suitable applying means.

The trimming means as shown in FIG. 6, comprise a pair of horizontally disposed cutter discs 50, 51 mounted for rotation by way of vertical shafts 52, 53 disposed in bearing means 54, 55 and driven by suitable means, not shown. A guide disc 56 is mounted on shaft 52 below cutter disc 50, with its peripheral edge slightly spaced from horizontally aligned cutter disc 51 to thereby position tab portion 15.

Guide means 57 of molded plastic or the like, passes the assembly of cable core 11 and envelope l2 to the cutter discs 50, 51. Thus, the tab portions are properly aligned for presentation to welding means 43. In the completed cable assembly, FIG. 8, the down turned tab portions 1ST of seam l4 lend themselves to further manipulation for electrical interconnection or termination of the envelopes 12 at the cable ends which are to be spliced or terminated.

I claim:

1. A method of forming an electrical cable comprising folding a metal tape about a cable core, said tape having a uniform wall thickness not exceeding about 0.30 mm. and a width greater than the circumference of said core, forming the marginal side portions of said folded tape into a pair of contacting tab portions extending radially of said core and having a height of from 4.0 to 8.0 mm., trimming the outer edges of said tab portions to provide freshly cut, oxide free edges, metallically integrating said oxide free edges of said tab portions only, bending said integrated tab portions at the base thereof and throughout the length thereof into contact with an outer surface portion of said tape, and applying a coating of metal adherent synthetic resin to the outer surface of said folded tape and tab portions for mechanically stiffening said thin metal tape.

2. A method as in claim 1, wherein said tape is aluminum, and said freshly cut oxide free edges thereof are immediately welded.

3. A method as in claim 2 and further including the step of applying a jacekting of synthetic resin over said metal adherent resin coating in bonded relation thereto. 

1. A method of forming an electrical cable comprising folding a metal tape about a cable core, said tape having a uniform wall thickness not exceeding about 0.30 mm. and a width greater than the circumference of said core, forming the marginal side portions of said folded tape into a pair of contacting tab portions extending radially of said core and having a height of from 4.0 to 8.0 mm., trimming the outer edges of said tab portions to provide freshly cut, oxide free edges, metallically integrating said oxide free edges of said tab portions only, bending said integrated tab portions at the base thereof and throughout the length thereof into contact with an outer surface portion of said tape, and applying a coating of metal adherent synthetic resin to the outer surface of said folded tape and tab portions for mechanically stiffening said tHin metal tape.
 2. A method as in claim 1, wherein said tape is aluminum, and said freshly cut oxide free edges thereof are immediately welded.
 3. A method as in claim 2 and further including the step of applying a jacekting of synthetic resin over said metal adherent resin coating in bonded relation thereto. 